The present invention relates to a radio telephone, and in particular to a radio telephone operable for more than one system.
Over the last ten years there has been a rapid growth in the use and availability of radio telephone systems. As part of this growth there has been a proliferation of different types of radio telephone system, offering the user a variety of services, geographical coverage and cost. Many of these different radio telephone systems cover the same, or a part of the same, geographical area as each other.
Typically, different radio systems operate on different radio frequencies, utilise different modulation techniques, signalling techniques and intra-system protocols etc. to each other. Thus, a radio telephone designed for one system is generally unable to be used on another system. Thus if a user wishes to have access to more than one system it is necessary to have either more than one radio telephone or a radio telephone capable of operating in more than one system. Having more than one radio telephone is inconvenient for the user. Known radio telephones capable of operating in more than one system typically consist of little more than 2 separate phones combined in a signal housing. The preference for operating in a particular system is user defined as disclosed in U.S. Pat. No. 4,989,230.
A particularly useful and appropriate environment for multi-mode radio telephones is the recently available cellular and cordless telephone systems. In the prior art, cordless telephones are typically used in the home and office to allow the user to place and receive calls at any point throughout the house via an RF link with a home base station located within the house or office. Such cordless telephones are connected via the home base station to the user""s telephone landline which in turn is connected to the Public Switched Telephone Network (PSTN). Further, there are known second generation cordless telephone systems such as CT-2 or DECT which are digital systems. Such CT-2 or DECT systems extend beyond conventional domestic operation of cordless telephones by allowing the user to establish an RF link between a CT-2 or DECT radio telephone and a base station in a more publicly accessible location e.g. outside of the user""s home, a railway station, shopping mall or airport. Such base stations are known as telepoint base stations and are linked to the PSTN in much the same way as a home base station. Some cordless, and in particular DECT radio telephones, are now able to receive calls via telepoint base stations whereas hitherto they were only able to place them. A description of such a system can be found in PCT international patent application WO 92/03006. Thus, placing and receiving calls whilst geographically roaming is possible in cordless telephone systems.
However, cordless telephone systems are low power systems and each base station provides telecommunications within only approximately a 150 meter radius of the base station, dependent upon the terrain and any man-made objects which could interfere with signalling between a cordless telephone and the base station. Such systems are generally only used in areas of high user density and thus tend to be limited to urban areas. This clearly restricts the geographical mobility of a CT-2, DECT or the like cordless telephone user.
In the prior art there are known so called cellular radio telephone systems having base stations which cover a wide geographical area (cell), eg 35 km diameter. However, in urban areas where the user density is high the cells are much smaller and operate at lower powers to facilitate frequency re-use thereby increasing the communication channel density.
Cellular systems have advantages over cordless systems since they allow a user to place and receive calls over a large area. Additionally they are suitable for use in moving vehicles. This is because cellular telephone systems have sophisticated handover procedures to facilitate switching between cells as a user""s vehicle crosses from one cell to another. Furthermore, the cells are larger than in cordless systems and thus handovers occur less often, even if travelling in a vehicle. This ensures continuity of service and is particularly important during a call. However, the cost of a cellular telephone call is significantly greater than the cost of a cordless telephone call, since cordless telephone calls are made by way of the user""s land line PSTN link and cost the same as landline calls, whilst cellular telephone calls are made by way of expensive cellular base stations and cellular switching equipment and cost much more than land line telephone calls. In order for a user to be able to utilise both cellular and cordless telephone systems via a single radio telephone handset a so-called cellular cordless telephone (CCT) has been proposed in U.S. Pat. No. 4,989,230. Both the cellular system and the cordless system are monitored by the CCT for incoming calls and the CCT automatically enters a user defined preferred mode for answering an incoming call if the system corresponding to that mode is available. When placing a call the user initiates the call as either cellular or cordless and the CCT connects the call appropriately. In order for the user to be able to make a choice the available systems can be displayed on the CCT. When using the CCT, the user has to make the decision as to which telephone system is used. Furthermore, the prior art CCT disclosed in U.S. Pat. No. 4,989,230 requires the user to select transfer of a cordless call to the cellular system should the cordless signals deteriorate (eg the user moves out of range of a cordless base station or the user""s velocity increases). Additionally, optimisation of the available systems is likely not to be achieved if the user is left to decide which system is to be used. One of the disadvantages of the CCT disclosed in U.S. Pat. No. 4,989,230 is that a user might not know if a signal is deteriorating until it is too late and the ongoing call is lost. For example, a visual indication of poor signal shown on the CCT is likely to be missed by a user, since in use the CCT will be placed at the side of the user""s head and thus visual indications would not be visible to the user. Other indications such as an audible tone or alarm would interfere with the user""s ongoing call, and would be annoying and irritating to the user.
A first aspect of the present invention provides a radio telephone operable in more than one radio telephone system, comprising communication means respectively associated with each of the more than one radio telephone system, monitoring means for monitoring signals of the more than one radio telephone system, and selection means responsive to said monitoring means for automatically selecting and re-selecting respective said communication means in accordance with the signals of one of the more than one radio telephone system fulfilling at least one predetermined criterion, and a second aspect of the invention provides a method for operating a radio telephone in more than one radio telephone system, comprising, monitoring signals of the more than one radio telephone system determining whether the signals of the more than one radio telephone system fulfill at least one predetermined criterion, and automatically selecting and re-selecting for which of the more than one radio telephone system the radio telephone is operable in accordance with the signals fulfilling the at least one predetermined criterion.
These have the advantage that the radio telephone is not only operable for more than one radio telephone system, but that it is able to automatically select and re-select which of the available radio systems to use. The selection can be based on any predetermined criterion or combination of criteria. For example, the radio telephone can be set to operate on the cheapest system available (e.g. cordless system). Such criteria are likely to be factory set, but optionally could be user programmable. A further advantage is that the radio telephone user can know of incoming calls on systems other than the one for which the radio telephone is presently operable, and can manually switch to operate in the appropriate system thereby overriding the automatic selection. Of course, if the radio telephone is already in a call then an indication that there is an incoming call can be made to the user (eg call waiting indication). Such a system would be of particular benefit if incoming calls from systems other than the one in which the radio telephone is currently operable were not forwarded to that system. An additional advantage is that automatic inter system handover would be possible, based on the predetermined criterion. For example, if the user were travelling out of a system service area and the service breaks down, a radio telephone operable in accordance with the present invention may automatically handover to a system having a good service (e.g. cordless to cellular). Similarly, if a user was engaged in a call on a high cost system and a low cost system became available such a radio telephone may automatically handover the call to the low cost system. Examples of inter-system handover are disclosed in co-pending British Patent Applications no. 9320814.8, no. 9320815.8 and no.9326169.1.
In a preferred embodiment of the first and second aspects of the invention there is provided a visual indication of the one of the more than one radio telephone system. This has the advantage that the user is informed of what radio systems are available. Thus, if the only radio systems available are ones which the user does not wish to use, the radio telephone can be turned off. This would avoid the problem of receiving calls on particularly expensive radio systems, if these radio systems were the only ones available.
Preferably, at least one predetermined criterion is a user indicated preference for one of said more than one radio telephone system. This has the advantage that the user can pre-program the radio telephone to select certain types of radio system, eg the cheapest available. Alternatively, the user indicated preference could be a manually indicated preference during operation of the radio telephone. Such a manually indicated preference could override any predetermined criteria and would give the user instantaneous control over which system the radio telephone is operable in at a given moment of time.
Suitably, at least one predetermined criterion can be one or a combination of the following requirements that the selected radio system is one for which:
i) the received signal strength at the radio telephone is greatest;
ii) the radio telephone has access rights;
iii) the selected radio telephone system requests selection;
iv) the bit error rate, frame error rate or the like is the lowest; and
v) the user velocity is appropriate.
These have the advantages in that the system for which there is a high probability of successful communication can be selected. Furthermore, the radio telephone can be set to select only those systems for which it has access rights thereby avoiding possible extra high costs for using a service for which no prior access arrangements have been made.
Advantageously, the monitoring means monitors the signals intermittently. Thus, less power is consumed by the radio telephone""s monitoring process which results in prolonged battery life. Furthermore, signals required to carry out the monitoring process are used less often which allows more time for the radio telephone to process signals for the currently operating radio system, in particular when a call is in progress. Intermittent monitoring is particularly effective during periods when no calls are in progress.
Typically, the radio system in which the radio telephone is operating will be a TDMA system and it would be advantageous if the monitoring process were carried out during a period of TDMA inactivity (eg unused slots). Thus, there would be none or at least reduced interference with the TDMA system signals. Additionally there is the benefit that the same components may be utilised for more than one terminal mode and so cost/size savings can be made. Both TDMA sharing of receiver functions between the systems and also transmitter functions can be utilised. By sharing transmitter functions, communications with a second system may start before releasing a first system.
In a third aspect of the invention there is provided a radio telephone system adapted to co-operate with at least one other radio telephone system, comprising user information exchange means respectively associated with each of the at least one other radio telephone system for exchanging user information signals between the radio telephone system and the at least one other radio telephone system, monitoring means for monitoring user information signals of the radio telephone systems and selection means for automatically assigning and re-assigning a user to one of the radio telephone systems in accordance with the user control signals fulfilling at least one predetermined criterion, and in a fourth aspect of the invention there is provided a method for operating a radio telephone system adapted to co-operate with at least one other radio telephone system, comprising, exchanging user information respectively associated with each of the at least one other radio telephone system between the radio telephone system and the at least one other radio telephone system, monitoring user information signals exchanged between the radio telephone systems, determining whether the user information signals fulfill at least one predetermined criterion, and automatically assigning and re-assigning a user to one of the radio telephone systems in accordance with the user information signals fulfilling the at least one predetermined criterion.
These have the advantage that users are automatically assigned or re-assigned to radio telephone systems dependent upon certain criteria being fulfilled. These criteria can be set by the radio systems themselves, or can be based on instructions from users. Since the radio telephone system exchanges user information between itself and other radio systems, the assigning and re-assigning of users to particular radio telephone systems can be made easily and quickly.
Additionally, calls from users can be routed through different radio telephone systems based on the predetermined criteria and the user information.